Every civilization has it's great moments history. And every civilization eventually falls just the same. There are no exceptions.
But what happens if an unknown force causes this to happen? What happens, if everything great, falls apart completely, leaving a corrupt government, with a ruler so vile and cruel that nopony dares to challenge.
Equestria is at this point in its' history, and there are very few that can correct it. 3 siblings, that don't even know each other, that were pried from their place in time, are forced into a situation to save Equestria from its' darkest sins.
The only problem, they hate each other.